The present invention relates generally to digital multimeters capable of performing multiple functions, such as the measurement of different electrical parameters and the performance of continuity and diode tests, and more particularly, to a multimeter having automatic function selection capability.
A digital multimeter having automatic function selection capability is disclosed in copending U.S. patent application Ser. No. 07/442,243 now U.S. Pat. No. 5,119,019, entitled AUTOMATIC FUNCTION SELECTING MULTIMETER, by Richard E. George and assigned to John Fluke Mfg. Co. Inc., the disclosure of which is hereby incorporated by reference.
It is believed that a multimeter formed in accordance with the present invention overcomes several shortcomings of a multimeter formed in accordance with copending application Ser. No. 07/442,243. The multimeter of the copending application requires a substantial number of additional hardware components that hinder attempts to reduce the size, complexity and cost of the multimeter. In addition, it is relatively slow to respond to changes in the type of analog input signal, which results in a noticeable time delay between changes in the analog input signal type and a display of the first correct reading of the new analog input signal. For example, when an AC signal is applied, the multimeter of the copending application will occasionally switch to DC volts and display a DC voltage reading before switching to the proper AC voltage measurement function. Accordingly, there is a need for a multimeter with improved automatic function selection capability, in that the multimeter provides this capability with the addition of very few components and is, therefore, inexpensive to manufacture, provides faster display updating and has a more stable display when a signal is first applied to the meter. The present invention is directed to an improved digital multimeter designed to achieve these results.